The present invention relates to an onsite method for treating contaminated drill cuttings before disposal and more particularly relates to a method for treating oil-contaminated drill cuttings at a solid offshore location so that the treated cuttings can be disposed of without ecological risk.
In a rotary drilling operation, a fluid commonly called "mud" is circulated from a storage area on the surface, downward through the drill pipe, out openings in the drill bit, and upward within the borehole to the surface. This return mud carries with it the drill cuttings from the bottom of the borehole. The returning mud along with its entrained drill cuttings is passed onto a "shale shaker" before it is returned to the storage area. The shaker which normally sits above the mud storage area is essentially a screen that is used to separate the drill cuttings and cavings from the mud. The mud falls by gravity through the screen and the cuttings pass over the end of the screen.
Disposal of these separated cuttings is sometimes a real problem, e.g. where the drilling operations are carried out at an offshore location. In some instances, the cuttings are merely passed from the shaker into the body of water and are allowed to settle to the bottom. However, as is often the case, when a drilling mud system such as an oil-base mud is used, the cuttings are usually coated with undesirable contaminants, e.g. oil. If these contaminated cuttings are disposed of directly into the water, there is a risk that free oil on the cuttings may wash off the cuttings and accumulate on the surface of the water. Due to this possible pollution threat, unless the cuttings can be ecologically disposed of, governmental regulations may prevent the use of oil-base muds in some drilling operations where the use of such muds is highly beneficial, if not mandatory.
There are at least two known general techniques for treating these contaminated cuttings to make them ecologically acceptable. Either they must be hauled or barged to disposal facilities on shore or they must be treated on site to remove the contaminants before they are disposed of in the water. The added expense involved in hauling the cuttings ashore is substantial, and, accordingly, seriously detracts from widespread commercial application of this technique. Further, the technique of hauling of the cuttings to shore for disposal may be impractical in areas of bad weather and rough seas. Therefore, for obvious reasons, it is much preferred to treat and dispose of the drill cuttings from offshore operations directly at the drilling site.
Several methods have been proposed for treating contaminated cuttings on site. One approach is to burn oil off the cuttings with high intensity lamps. However, this approach presents problems (i.e., possible fire hazards due to the lamps and the difficulty of equally exposing all the cuttings to the lamps) which makes it unfeasible in most instances.
Another approach involved washing the cuttings with a detergent to remove the contaminants, separating the washing solution and contaminants, and dumping the cleaned cuttings into the water. One example of this approach is disclosed in U.S. Pat. No. 3,688,781, issued Sept. 5, 1972. Other wash techniques are discussed in the article "Cuttings Can Meet Offshore Environment Specifications", OIL AND GAS JOURNAL, Aug. 14, 1972, pp. 73-76. While such techniques may be successful in cleaning the cuttings, the handling and disposal of large volumes of wash solution and the equipment necessary for washing the cuttings detract from the overall effectiveness of this method. Therefore, a reliable method for treating oil contaminated cuttings onsite is needed to insure the oil base muds can be safely used in all instances where drilling conditions dictate their use.